Various techniques are known for applying molten solder to a PCB having through-hole mounted components to effect soldering and/or desoldering operations. Of the known devices, they generally fall into two categories. The first consists of a solder bath where a container is provided for the molten solder and the solder simply sits in the container, there being no movement of the solder. The leads of the components to be removed are dipped into the bath to effect either soldering or desoldering thereof. This technique is unsatisfactory in that the entire surface area of the solder is exposed to the air and tends to be oxidized thus forming contaminants for the above operations. Further, other contaminants may be introduced into the upper surface of the bath due to the soldering and/or desoldering operations. In a relatively short time the dross (as the above contaminants are sometimes collectively called) must be removed in order not to compromise the soldering/desoldering operations or other means must be used to accommodate this problem.
In another system, a fountain effect is provided whereby the solder is raised through a first path through an opening to form a fountain which contacts the area of the PCB to be processed, the solder then being returned to the main solder supply via a second path. Such a device is disclosed in U.S. Pat. No. 4,162,034. Such devices also involve a large exposure of the solder to the ambient air thus introducing a large degree of oxidation which ultimately shortens the useful life of the solder supply. Hence, the solder supply must be relatively frequently replaced in order not to compromise the integrity of the soldering/desoldering process.
Other prior art directed to the use of molten solder for soldering and desoldering operations includes U.S. Pat. Nos. 2,986,108; 3,990,621; 3,993,235; 4,315,590; 4,412,641; 4,437,605; and 4,523,708.
The soldering/desoldering device described in the above related application Ser. No. 763,704 is characterized in one aspect thereof in that the solder is raised to the upper surface of a hollow applicator having an open top. The mechanism employed for raising the solder is a piston and cylinder type arrangement. Although this arrangement is useful in certain applications, it does have a drawback in other applications such as soldering or desoldering. That is, when soldering or desoldering, the PCB is placed above the applicator and means are employed to hold it in place. However, since the solder is raised to the uppermost level within the applicator and since it is sometimes difficult to control the pressure exerted by the piston and cylinder arrangement, there is at times a tendency for the solder to break through the holes and flow onto the upper surface of the board. Moreover, the piston often tends to bind in this type of application.
In order to solve the foregoing problem one aspect of the present invention is to employ pneumatic means for raising the solder to the uppermost level of the applicator. Accordingly, the pressure can be very accurately controlled to prevent solder breaking through the holes of the PCB. Other prior art devices have employed pneumatic means in connection with soldering/desoldering utilizing molten solder such as the above mentioned U.S. Pat. No. 4,162,034. However, as stated above, the foregoing patent is directed to the formation of a fountain which flows against the area of the PCB to be processed. The disadvantages of this process in terms of contamination of the solder have been discussed above. This contamination problem is overcome in the above mentioned related application and in the present invention in that the surface area of the solder normally exposed to the atmosphere is quite small compared to the total service area of the solder employed in the system. Further, the solder is raised to the top of the applicator only when needed for a soldering/desoldering operation or other special operation. It is immediately lowered after the operation and thus, for this further reason, contamination of the solder is kept to a minimum. The latter system is known as a dynamic balance system in that the solder is dynamically balanced at the uppermost level of the nozzle during soldering/desoldering. This is in contradistinction to the static solder bath or the free flowing fountain types of systems. The use of pneumatic pressure in a dynamic balance system overcomes not only the problems associated with U.S. Pat. No. 4,162,034 but also those which are occasionally encountered in the system of the related application Ser. No. 764,704.